This invention relates to a method for detecting analyte moieties by means of a signalling moiety, and particularly by means of a signalling moiety that can aggrandize or be aggrandized.
Assay systems for the detection of analyte moieties of biomedical interest have been known for a number of years. These systems include, for example, immunodiffusion, immunoelectrophoresis, agglutination, and immunofluorescence. These systems variously have limitations in convenience, sensitivity, ease of sample preparation, adaptability to automation, and applicability to various specific analyte moieties.
Radioimmunoassay (RIA) represents a convenient, sensitive, flexible, and easily automatable method for the detection. The disadvantages of RIA detection systems relates to the problems inherent in the use of radioisotopes, which provide the signal in RIA's. The problems include, variously, high cost and short storage life of the radiolabeled reagents, the requirement for special equipment for detection of the signal, the health hazard to laboratory personnel, and the expense and inconvenience of disposal of the radioactive waste.
Recently, a sensitive and convenient method for detection has been introduced, which does not require the use of radioisotopes. The enzyme-linked immunosorbent assay (ELISA) makes use of enzymes as signalling moieties. The sensitivity of ELISA is limited, in part, by the number of enzyme molecules that can be attached to the analyte-specific moiety used. When an analyte moiety is capable of growth (e.g. a bacterium), it is often advantageous to grow it, either in vivo or in vitro to make the task of detection easier. Following growth, the analyte moiety can be detected by means of observing any of its physical or metabolic characteristics for example, its cellular or colonial morphology, nutritional requirements, metabolic products, staining characteristics or potential for pathogenesis. As few as one viable bacterial cell can be detected in this way.
The ability of bacteria to grow has made them useful signalling moieties for the detection of other moieties. When the ability of the bacterium to grow is dependent upon the analyte moiety (e.g. when the bacteria are auxotrophic for the analyte moiety), the growth of the bacteria can be used to detect the presence of the analyte moiety. The growth of the bacteria is stoichiometrically related to the amount of analyte moiety present. Of course, this type of bioassay is limited to specific signalling moiety-analyte moiety pairs.